Mothers pass antibodies against measles to their babies in the womb, but the protection disappears quicker than previously thought, with most infants becoming susceptible to measles by 3 months, according to a study published Nov. 21 in Pediatrics.
Researchers checked blood samples for measles antibody levels in 196 infants younger than 12 months at the Hospital for Sick Children in Toronto. Thirty-five percent of babies had underlying medical conditions, though children with immune system diseases were excluded.
In the first month, 20 percent of infants had antibody levels below the protective threshold. By three months, 92 percent of infants were not protected against measles. At six months, none of the infants were protected against the virus
"Prior to this research, in general, it was assumed that infants were immune to measles for at least the majority of their first 6 months of life," study authors Michelle Science, MD, an infectious disease consultant at the Hospital for Sick Children, and Shelly Bolotin, a scientist at Public Health Ontario, told STAT. "Our findings have revealed a wide susceptibility gap between the time that infants lose the protection that they've received from their mother and when they are protected by vaccination at 12 months."
The authors said there isn't an easy way to remedy this susceptibility. If vaccinated before 12 months, babies don't develop as strong of an immune response from the vaccine, Dr. Science and Ms. Bolotin told STAT. It's also not possible to give pregnant women booster shots because the vaccine contains a live virus, which are generally not given to expecting mothers.
"One of the best ways to protect young infants is to make sure those around them are vaccinated. This not only protects infants but also other groups who are vulnerable to measles, such as immune-compromised individuals who cannot be vaccinated," Dr. Science and Ms. Bolotin told STAT.